Hard disk drive (HDD) electrical over voltage stress (EOS) systems and methods

ABSTRACT

The present invention relates to a hard disk drive system having overvoltage protection circuits for various types of overvoltage conditions. For example, the system includes one or more hard disk drive integrated circuit chips residing on a board and a hard disk drive power plug receptacle residing on the board having two different value power supply ports associated therewith. The receptacle is operable to receive a power plug therein, wherein when the power plug is inserted therein in a proper orientation the two different value voltages are properly supplied to the one or more hard disk drive integrated circuit chips, and wherein when the power plug is inserted therein in an improper orientation the two different value voltages are switched with respect to their intended values.

This application is a division of application Ser. No. 10/449,240, filedMay 30, 2003, now abandoned, which is a division of application Ser. No.09/735,013, filed Dec. 12, 2000, now abandoned.

FIELD OF THE INVENTION

The present invention relates to electronic circuits and, moreparticularly, to a circuit, system, structure and method for reducing orotherwise eliminating electrical over voltage stress (EOS) relatedfailures in hard disk drive (HDD) systems and boards as discussed, andin addition, other memory storage devices such as floppy disk drives,removable hard disk drives, tape drives, CD drives, and DVD drives.

BACKGROUND OF THE INVENTION

Hard disk drives such as the exemplary drive 10 illustrated in FIG. 1 ainclude one or a stack of magnetically coated platters 12 that are usedfor storing information. The magnetically coated platters 12 are mountedtogether in a stacked position through a spindle 14 which may bereferred to as a platter stack. The platter stack is typically rotatedby a motor that is referred to as a spindle motor or a servo motor (notshown). A space is provided between each platter to allow an arm 18having a read/write head or slider 20 associated therewith to bepositioned on one or both sides of each platter 12 so that informationmay be stored and retrieved. Information is stored on one or both sidesof each platter 12 and is generally organized into sectors, tracks,zones, and cylinders.

Each of the read/write heads or sliders 20 are mounted to one end of thededicated suspension arm 18 so that each of the read/write heads may bepositioned as desired. The opposite end of each of the suspension arms18 are coupled together at a voice coil motor 16 (VCM) to form one unitor assembly (often referred to as a head stack assembly) that ispositionable by the voice coil motor. Each of the suspension arms 18 areprovided in a fixed position relative to each other. The voice coilmotor 16 positions all the suspension arms 18 so that the activeread/write head 20 is properly positioned for reading or writinginformation. The read/write heads 20 may move from at least an innerdiameter to an outer diameter of each platter 12 where data is stored.This distance may be referred to as a data stroke.

Hard disk drives also include a variety of electronic circuitry 30 forprocessing data and for controlling its overall operation as illustratedin FIG. 1 b. This electronic circuitry 30 may include a pre-amplifier32, a read channel/write channel circuit 33, a servo controller 34, amotor control circuit 35, a read-only memory 36 (ROM), a random-accessmemory 37 (RAM), and a variety of disk control circuitry such as an HDDcontroller 38 or microprocessor to control the operation of the harddisk drive and to properly interface the hard disk drive to a system bus39, and voltage regulators to supply voltages needed other than the onesfrom the power plug. The pre-amplifier 32 may contain a readpre-amplifier and a write pre-amplifier that is also referred to as awrite driver. The pre-amplifier 32 may be implemented in a singleintegrated circuit or in separate integrated circuits such as a readpre-amplifier and a write pre-amplifier or write driver. The diskcontrol circuitry 38 generally includes a separate microprocessor forexecuting instructions stored in memory to control the operation andinterface of the hard disk drive.

Hard disk drives perform write, read, and servo operations when storingand retrieving data. The preamplifier circuit IC is located proximate tothe arms 18 and a flex 50 is used to couple the signals back and forthto the remaining circuitry on a printed circuit board (PCB) 52 (see,e.g., FIG. 2 b). The PCB 52 contains the remaining circuitry of FIG. 1 band receives power from a power plug into a receptacle. An exemplaryplan view of a plug receptacle or socket is illustrated in FIG. 2 c, anddesignated at reference numeral 54. The non-portable PC industrystandard socket 54 will comprise a four pin male type connector forproviding supply voltage potentials of 5V, GND, GND and 12V,respectively, to the PCB circuitry.

The non-portable PC industry standard socket 54 further includes two 45degree filled corner tabs 56 which serve as a key to discourage plugginga power plug into the socket 54 in the wrong way, for example, reversingthe plug. Unfortunately, in some cases it is still possible to force thepower plug into the socket 54 in an improper orientation if sufficientforce is exerted on the power plug. In such cases, the 5V and 12V supplyvoltages are switched, and circuitry intended to receive 5V may receive12V, which may result in an electrical overvoltage stress (EOS) relatedcircuit failure.

The 5V only or 3.3V only (no 12V) HDDs for portable PCs use a differentpower plug configuration. In the non-portable use, a 5V HDD with adifferent plug configuration may use a socket adapter to thenon-portable industry standard socket 54, and there the possibility ofreverse plugging the socket adapter still exists.

In addition, the circuitry on the PCB 52 is powered by system powersupplies not located thereon which may not be adequately regulated or,in some cases, may be defective. Such system conditions may result inovervoltage conditions at either or both of the 5V and 12V pins,respectively, even when the power plug is properly inserted into thesocket 54. Such overvoltage conditions may also contribute to EOSrelated circuit failures.

SUMMARY OF THE INVENTION

The present invention relates generally to circuitry for protecting harddisk drive systems from undesirable voltage conditions due to, forexample, a reverse power plug condition or an unregulated or otherwisemalfunctioning power supply. For example, FIGS. 3 and 5 are twodifferent implementations of V5 protection; and FIGS. 6 and 7 are twodifferent implementations of V12 protection. Each of theseimplementations provide different levels of protection and V5 and V12protection may be implemented together or independently of one another,as may be desired.

According to one aspect of the present invention, a hard disk driveprotection system comprises a reverse power plug orientation protectioncircuit (see, e.g., FIG. 3). The protection circuit is operable todetect an improper orientation of a power plug in a power plugreceptacle or socket on a hard disk drive printed circuit board. Upondetection of the improper orientation, the protection circuit is furtheroperable to reduce the voltage provided to a circuit board trace whichis intended to carry a relatively low power supply potential to one ormore integrated circuit chips on the board. In the above manner, anovervoltage condition associated with an improperly oriented power plugis mitigated or otherwise eliminated.

According to another aspect of the present invention, the reverse powerplug orientation circuit comprises a variable resistance circuit whichis operable to vary a resistance associated therewith as a function ofthe power plug orientation. For example, when the power plug is properlyinserted into the power plug socket (see, e.g., FIG. 4 a), the variableresistance circuit approximates a short circuit with negligibleresistance to substantially pass a supply voltage to associated harddisk drive components on the printed circuit board. Alternatively, whenthe power plug is reversed and improperly oriented within the power plugsocket (see, e.g., FIG. 4 b), the variable resistance circuit exhibits asubstantial resistance, thereby causing a substantial voltage dropthereacross and thus reduces a voltage which is passed to hard diskdrive components on the printed circuit board. Consequently, anovervoltage condition associated with a reversed power plug is mitigatedor eliminated altogether.

According to another aspect of the present invention, the variableresistance circuit comprises a transistor having a control terminalcoupled to a pin associated with the high supply voltage potential whenthe power plug is properly oriented in the socket and another terminalcoupled to a pin associated with a low supply voltage potential when thepower plug is properly oriented. Under normal conditions, the highsupply potential activates the transistor causing it to approximate ashort circuit. Under adverse conditions when the power plug isimproperly oriented in the power plug, the supply potentials areswitched and the low supply potential is coupled to the transistorcontrol terminal, thereby decreasing the conduction and increasing theresistance thereof. Consequently, the high supply potential present atthe transistor is reduced thereacross, thus preventing the highpotential from being transmitted undesirably to one or more circuitcomponents on the hard disk drive printed circuit board.

According to still another aspect of the present invention, anovervoltage protection circuit (see, e.g., FIG. 5) is disclosed which isoperable to prevent circuit damage due to reverse plugging or anunregulated or defective 5V power supply in a hard disk drive system.The overvoltage protection circuit comprises a voltage detection circuitwhich is operable to monitor a voltage associated with the low supplyvoltage, and output an activation signal when the voltage associatedtherewith exceeds a predetermined level. The overvoltage protectioncircuit further comprises a voltage reduction circuit operably coupledto the voltage detection circuit, and operable to reduce a value of thelow supply voltage upon receipt of the activation signal from thevoltage detection circuit. Upon activation, the voltage reductioncircuit increases a resistance in a transmission path between the lowvoltage supply and the hard disk drive components, thereby generating avoltage drop there across and reducing the voltage seen at the systemcomponents.

According to yet another aspect of the present invention, the voltagedetection circuit comprises a zener diode in series with a resistor.When the low supply voltage exceeds a predetermined level, the reversebiased zener diode reaches its zener breakdown voltage and breaks down,causing current to conduct therethrough. The current conduction causes avoltage drop to occur across the resistor which is then used as anactivation signal to indicate that an overvoltage condition has beendetected.

According to still another aspect of the present invention, the voltagereduction circuit (see, e.g., FIG. 6) comprises a transistor having acontrol terminal coupled to the voltage detection circuit. Upondetection of an overvoltage condition of the 12V power supply, anactivation signal from the voltage detection circuit causes thetransistor to turn on. The transistor is connected to a control terminalof another transistor which is within the transmission path between thesupply voltage being monitored and the hard disk drive components. Whenthe first transistor turns on, the voltage and the control terminal ofthe second transistor in the transmission path goes low, causing it tobecome more resistive. The increased resistance in the transmission pathresults in a reduced voltage at the hard disk drive components, therebyreducing failures associated with electrical overstress (EOS)conditions.

According to still another aspect of the present invention, anovervoltage protection circuit (see, e.g., FIG. 7) is disclosed which isoperable to prevent circuit damage due to an unregulated or defective12V power supply in a hard disk drive system. The overvoltage protectioncircuit comprises a voltage detection circuit which is operable tomonitor a voltage associated with the high supply voltage, and output anactivation signal when the voltage associated therewith exceeds apredetermined level. The overvoltage protection circuit furthercomprises a voltage reduction circuit operably coupled to the voltagedetection circuit, and operable to reduce a value of the high supplyvoltage upon receipt of the activation signal from the voltage detectioncircuit. Upon activation, the voltage reduction circuit increases aresistance in a transmission path between the high voltage supply andone or more of the hard disk drive components, thereby generating avoltage drop thereacross and reducing the voltage seen at the one ormore system components.

According to yet another aspect of the present invention, the voltagereduction circuit uses a pass FET already associated with the hard diskdrive system to reduce the voltage when a voltage associated with thehigh voltage supply exceeds a predetermined threshold. When anovervoltage condition is detected, the pass FET becomes less conductingor more resistive, thereby causing a voltage drop thereacross andreducing the value associated with the first supply voltage at thetrace. In addition, a second transistor may be configured in series withthe pass FET such that backgate diodes associated therewith and the passFET are oriented in a back-to-back configuration. Such back-to-backbackgate diodes prevent conduction therethrough under large overvoltageconditions associated with the first supply voltage.

To the accomplishment of the foregoing and related ends, the inventioncomprises the features hereinafter fully described and particularlypointed out in the claims. The following description and the annexeddrawings set forth in detail certain illustrative embodiments of theinvention. These embodiments are indicative, however, of but a few ofthe various ways in which the principles of the invention may beemployed and the present invention is intended to include all suchembodiments and their equivalents. Other objects, advantages and novelfeatures of the invention will become apparent from the followingdetailed description of the invention when considered in conjunctionwith the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a perspective view of a prior art disk drive mass storagesystem;

FIG. 1 b is a schematic diagram illustrating circuitry associated with adisk drive mass storage system;

FIG. 2 a is a plan view illustrating a platter having a servo wedgeassociated therewith for use in positioning a read/write head accuratelythereon;

FIG. 2 b is a perspective view of a portion of a disk drive systemillustrating the circuitry associated with the disk drive mass storagesystem;

FIG. 2 c is a plan view of a power plug receptacle or socket having akey portion for guiding a power plug orientation associated therewith;

FIG. 3 is a schematic diagram illustrating a reverse plug orientationprotection circuit according to one aspect of the present invention;

FIG. 4 a is a schematic diagram illustrating the protection circuit ofFIG. 3 under normal power plug orientation conditions;

FIG. 4 b is a schematic diagram illustrating the protection circuit ofFIG. 3 under adverse conditions where the power plug orientation in thesocket has been reversed;

FIG. 5 is a schematic diagram illustrating a reverse plug orientationand an overvoltage protection circuit associated with a low voltagepower supply according to another aspect of the present invention;

FIG. 6 is a schematic diagram illustrating an overvoltage reductioncircuit associated with a high voltage power supply according to yetanother aspect of the present invention; and

FIG. 7 is a schematic diagram illustrating an overvoltage protectioncircuit associated with the high voltage power supply according to stillanother aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described with respect to theaccompanying drawings in which like numbered elements represent likeparts. The present invention relates to a system and circuitry forpreventing overvoltage conditions on a hard disk drive printed circuitboard.

Turning now to the figures, FIG. 3 is a combined block level andschematic diagram illustrating an electrical over stress protectionsystem 100 according to one exemplary aspect of the present invention.The system 100 may reside on a hard disk drive printed circuit board(PCB) which includes a hard disk drive power plug receptacle or socket102. According to one exemplary aspect of the present invention, thenon-portable PC industry standard receptacle or socket 102 is a four pinmale type adapter having a pin for a high, first supply voltage value(e.g., about 12V), two pins for circuit ground potential value, and apin for the second, low supply voltage value (e.g., about 5V),respectively. Regulator circuitry 104 may be coupled to a fourth pin 106of the adapter 102 to provide voltage regulation for the other supplyvoltages used within the PCB. A reverse plug orientation protectioncircuit 108 is coupled between the adapter 102 and other hard disk driveboard components (e.g., integrated circuit chips) via one or more supplyvoltage traces 110. The protection circuit, according to one exemplaryaspect of the present invention, is also coupled to the first supplyvoltage value via a first pin 112 of the adapter 102.

According to an exemplary aspect of the present invention, theprotection circuit 108 is operable to detect an improper orientation ofa power plug when inserted into the receptacle or socket adapter 102 andthen reduce a voltage value at the one or more traces 110 in response tothe detection. For example, the protection circuit 108 may comprise avariable resistor circuit which is operable to adjust a resistance valueassociated therewith based on the orientation of a power plug in thepower plug socket 102. Under normal operating conditions when the powerplug is properly oriented in the socket 102, the variable resistancecircuit exhibits substantially no resistance and approximates a shortcircuit to pass the second supply voltage value to the trace 110 withouta substantial voltage drop thereacross. Under other conditions, however,when the power plug is reversed and plugged into the socket 102 in animproper orientation, the variable resistance circuit exhibits asubstantial resistance, thereby causing a voltage drop thereacross tothereby prevent an undesirable high voltage value form appearing on theone or more traces 110.

Any type of circuitry which may provide the above functionality may beutilized as the protection circuit 108, and such variations arecontemplated as falling within the scope of the present invention. Forexample, according to one aspect of the present invention, theprotection circuit 108 comprises a transistor such as an NMOS transistor114 as illustrated in FIG. 3. In operation, the transistor works asfollows, as illustrated in FIGS. 4 a and 4 b, respectively. In FIG. 4 a,the power plug is inserted into the socket 102 in the proper orientationsuch that the first supply voltage value is provided to the first pin112 (e.g., 12V) and the second supply voltage value is provided to thefourth pin 106 (e.g., 5V), respectively. As seen in FIG. 4 a, thisresults in 12V being applied to a control terminal (e.g., a gate) of thetransistor 114, causing it to substantially turn on (e.g., fullconductance). In such a state, the transistor 114 approximates a shortcircuit and almost all of the 5V is passed from the fourth pin 106 ofthe socket 102 to the one or more traces 110.

Alternatively, when the power plug is inserted into the socket 102 in animproper orientation, the first and second supply voltage values areswitched on the pins 106 and 112, as illustrated in FIG. 4 b. That is,the higher voltage (e.g., 12V) now appears on the fourth pin 106 andwithout the help of the transistor 114, would result in a high andpotentially damaging voltage appearing on the one or more traces 110which go to various circuit components on the board. However, accordingto the present invention, the transistor 114 now has the lower voltagevalue (e.g., 5V) on its gate terminal, thus causing the conductancethereof to be substantially diminished. That is, the resistanceassociated with the transistor 114 is substantial and therefore asignificant voltage drop (ΔV>0V) will occur across the transistor 114,thereby reducing the voltage on the one or more traces 110 (e.g., ΔV isequal to about 7–8V, thus leaving about 4V at the trace 110.).

According to another aspect of the present invention, a reverse plugorientation and an overvoltage protection circuit is disclosed, asillustrated in FIG. 5 and designated at reference numeral 150. Theovervoltage protection circuit 150 is operable to reduce the voltage atthe 5V board trace 110 under system conditions when the 5V supplyvoltage exceeds its rated voltage (e.g., increasing substantially above5V) due to, for example, an unregulated or defective 5V supply.According to one exemplary aspect of the present invention, theovervoltage protection circuit 150 comprises a voltage detection circuit152 and a voltage reduction circuit 154, respectively. The voltagedetection circuit 152 is operable to detect a circuit condition in whichthe potential of a 5V supply 156 exceeds a predetermined level, forexample, some value greater than 5V. Upon detection of such a circuitcondition, the voltage detection circuit 152 provides an activationsignal to the voltage reduction circuit 154 which is operable to reducethe voltage associated with the 5V supply 156 at the trace 110 whichsupplies the supply potential to at least one of the various integratedcircuit chips on the hard disk drive printed circuit board.

In accordance with one exemplary aspect of the present invention, thevoltage detection circuit 152 may comprise a zener diode 158 in serieswith a resistor 160. In operation, under normal conditions when thesupply voltage is about 5V, the voltage across the zener diode 158 isreverse biased and the diode 158 is nonconducting. Under an overvoltagecondition, however, where the potential of the 5V supply 156 exceedssubstantially its rated voltage, the zener diode is reverse biased andbreaks down (e.g., by setting the zener breakdown voltage at about thepredetermined level which is greater than 5V) and current conductstherethrough. Based upon the breakdown current, the resistor 160develops a voltage thereacross which serves as an activation signal thatan overvoltage condition has been detected. Although the zener diode andresistor combination has been illustrated and described as one type ofvoltage detection circuit, other types of circuits may be employed toprovide similar voltage detection functionality and such alternativecircuitry is contemplated as falling within the scope of the presentinvention.

In accordance with another exemplary aspect of the present invention,the voltage reduction circuit 154 may comprise a transistor 162 such asan NPN type bipolar transistor having a control terminal coupled to thevoltage detection circuit 152. The voltage reduction circuit 154 alsomay include a resistor 164 coupled in series between another, highervalue voltage supply 165 (e.g., a 12V supply) and a control terminal ofanother transistor 166, for example, an NMOS transistor. Under normaloperating conditions, no activation signal is provided by the voltagedetection circuit 152 to the voltage reduction circuit 154, and thus theNPN transistor 162 is off. With no current conduction through transistor162, the resistor 164 conducts substantially no current and passeseffectively the voltage potential of the supply 165 to the gate of thetransistor 166. With the gate of the transistor 166 being high, thetransistor 166 is conducting and the 5V supply potential is transmittedsubstantially to the trace(s) 110.

Under a detected overvoltage condition, however, the voltage detectioncircuit 152 provides an activation signal to the base of the transistor162, thus turning the transistor 162 on and initiating currentconduction therethrough. As current conducts through the NPN transistorbase 162, a voltage drop occurs across the resistor 164 due to thecurrent conduction therethrough, thus causing the gate voltage of theNMOS transistor 166 to decrease, resulting in decreased currentconduction through the transistor 166. As the NMOS transistor 166becomes more resistive, a voltage drop occurs thereacross, therebydecreasing the voltage supplied by the 5V supply 156 to the trace(s)110. In the above manner, the voltage reduction circuit 152 operates toreduce the voltage at the trace(s) 110 when an overvoltage condition atthe supply 156 is detected. Although FIG. 5 illustrates one exemplaryvoltage reduction circuit, various types of other circuit components andconfigurations may be employed to provide such functionality and suchalternative circuits are contemplated as falling within the scope of thepresent invention.

According to yet another aspect of the present invention, an overvoltageprotection circuit is disclosed for protecting against an overvoltagecondition associated with the high voltage supply (e.g., 12V supply), asillustrated in FIG. 6 and designated at reference numeral 200. Accordingto one exemplary aspect of the present invention, the overvoltageprotection circuit 200 advantageously utilizes a pass FET 202 whichalready exists on the hard disk drive printed circuit board, however,use of such pass FET 202 is not required, and other switching componentsor circuits may be utilized and are contemplated as falling within thescope of the present invention.

The overvoltage reduction circuit 200 in FIG. 6 is operable to reducethe board motor voltage to the servo IC 204, the servo driver FETs 206and the servo IC motor voltage 208 under system conditions when the 12Vsupply voltage 210 exceeds its rated voltage (e.g., increasing slightlyabove 12V). According to one exemplary aspect of the present invention,the overvoltage protection circuit 200 comprises a voltage detectioncircuit 220 and a voltage reduction circuit 222, respectively. Thevoltage detection circuit 200 is operable to detect a circuit conditionin which the potential of the 12V supply 210 exceeds a predeterminedlevel, for example, some value greater than 12V. Upon detection of sucha circuit condition, the voltage detection circuit 220 provides anactivation signal to the voltage reduction circuit 222 which is operableto reduce the voltage associated with the 12V supply 210 at the traces204, 206 and 208, respectively, which supplies the supply potential toat least one of the various integrated circuit chips on the hard diskdrive printed circuit board.

In accordance with one exemplary aspect of the present invention, thevoltage detection circuit 220 may comprise a zener diode 230 in serieswith a resistor 232. In operation, under normal conditions (the supply210 properly supplying 12V) the voltage across the zener diode 230 isreverse biased and nonconducting. Under an overvoltage condition,however, where the potential of the 12V supply 210 exceeds its ratedvoltage, the zener diode 230 is reverse biased and breaks down (e.g., bysetting the zener breakdown voltage at about the predetermined levelwhich is slightly greater than 12V, for example, about 13V) and currentconducts therethrough. Based upon the breakdown current, the resistor232 develops a voltage thereacross which serves as an activation signalthat an overvoltage condition has been detected. Although the zener andresistor combination has been illustrated and described as one type ofvoltage detection circuit, other types of circuits may be employed toprovide similar voltage detection functionality and any such circuitryis contemplated as falling within the scope of the present invention.

In accordance with another exemplary aspect of the present invention,the voltage reduction circuit 222 may comprise a transistor 240 such asan NPN type bipolar transistor having a control terminal coupled to thevoltage detection circuit 220. The voltage reduction circuit 222 alsoincludes the pass FET 202 having a control terminal coupled to the NPNtransistor 240. The control terminal of the pass FET 202 is also coupledto supply disconnect sense circuit 250 which is operable to detect asystem condition where the 12V supply has been disconnected from thehard disk drive system. Under such conditions, the sense circuit 250turns off the pass FET 202 to enable the back EMF of the motor (notshown) to be used as a power source to park the head into its properlanding zone via the servo IC 204 in the absence of the 12V supplyvoltage.

The overvoltage circuit 200 operates in the following exemplary manner.Under normal operating conditions, no activation signal is provided bythe voltage detection circuit 220 to the voltage reduction circuit 222,and thus the NPN transistor 240 is off. With no current conductionthrough transistor 240, the pass FET 202 remains conducting via thesense circuit 250 (when the sense circuit 250 does not detect an absenceof the 12V supply). With the gate of the pass FET 202 high, thetransistor 202 is conducting and the 12V supply potential is transmittedsubstantially to the trace(s) 204, 206 and 208, respectively.

Under a detected overvoltage condition, however, the voltage detectioncircuit 220 provides an activation signal to the base of the transistor240, thus turning the transistor 240 on and pulling the gate of the passFET 202 low. As the gate voltage of the pass FET 202 decreases, the passFET 202 becomes more resistive, and a voltage drop occurs thereacross,thereby decreasing the voltage supplied by the 12V supply 210 to thetrace(s) 206 and 208. The resistor 281 serves to limit power dissipationand voltage to other PCB components. In the above manner, the voltagereduction circuit 222 operates to reduce the voltage at the trace(s) 206and 208 when an overvoltage condition at the 12V supply 210 is detected.Although FIG. 6 illustrates one exemplary voltage reduction circuit,various types of other circuit components and configurations may beemployed to provide such functionality and such alternative circuits arecontemplated as falling within the scope of the present invention.

In accordance with another aspect of the present invention, theovervoltage protection circuit 200 further comprises a reset circuit 260which is operable to output a reset signal in response to a detected 12Vsupply overvoltage condition. According to one exemplary aspect of thepresent invention, the reset circuit 260 comprises a transistor 262, forexample, an NPN type bipolar transistor having a control terminalcoupled to the voltage detection circuit 220. When the voltage detectioncircuit 220 detects an overvoltage condition associated with the 12Vsupply 210, the activation signal (e.g., the voltage across the resistor232) is output to the reset circuit 260. The activation signal isoperable to turn the transistor 262 on and pull an output 264 thereof,labeled RESETZ down to a circuit ground potential.

According to an exemplary aspect of the present invention, RESETZ is areset signal that goes to the hard disk drive microprocessor or ASICcontroller (not shown), depending on the hard disk drive systemconfiguration being employed, which turns off the servo motor and parksthe head in its appropriate landing zone. The microprocessor orcontroller will then re-initiate the hard disk drive system start-upprocess using any one of various well known initialization procedures.Although the above reset circuit 260 is described in conjunction with atransistor 262, other circuits providing similar functionality may beemployed and such alternatives are contemplated as falling within thescope of the present invention.

In the above example, the circuit 200 operates well when the 12V supply210 experiences an overvoltage condition which is not substantiallygreater than the rated supply voltage of about 12V. In cases where the12V supply potential greatly exceeds its rated voltage (e.g., about30V), the circuit 200 has some potential limitations. For example, thediode (not shown) which is implicit in the pass FET 202 (the backgatediode) will tend to conduct when the voltage from the supply 210 isgreater than the board motor voltage VM 206. Consequently, the voltageat the traces 206 and 208 will get clamped at about a backgate diodedrop (e.g., about 1V) below the supply potential 210. For supplypotentials not substantially greater than 12V (e.g., about 13–15V) suchprotection may be acceptable, however, for supply voltages substantiallygreater, large potentially undesirable voltages may still appear on thetraces 206 and 208, respectively.

According to still another aspect of the present invention, a circuitfor protecting against substantial overvoltage conditions on the highvoltage supply is disclosed in FIG. 7, and designated at referencenumeral 280. The overvoltage protection circuit 280 is similar in manyrespects to the circuit 200 of FIG. 6, however, the circuit 280 of FIG.7 has a voltage reduction circuit 290 that differs from the voltageprotection circuit 222 of FIG. 6. The voltage protection circuit 290 hasa second transistor 292, for example, an NMOS transistor, in series withthe pass FET 202 such that their backgate diodes are coupled together ina back-to-back series fashion (e.g., cathode to cathode). In the abovemanner, when the 12V supply voltage 210 increases substantially aboveits rated voltage, although the backgate diode associated with the passFET 202 becomes forward biased, the second backgate diode associatedwith the transistor 292 is reverse biased and no current conductstherethrough. Consequently, a substantial portion of the voltage isdropped across the reverse biased backgate diode of transistor 292, thusprotecting the traces 206 and 208 from experiencing a potentiallyundesirable high voltage thereat.

Although the invention has been shown and described with respect to acertain preferred embodiment or embodiments, it is obvious thatequivalent alterations and modifications will occur to others skilled inthe art upon the reading and understanding of this specification and theannexed drawings. In particular regard to the various functionsperformed by the above described components (assemblies, devices,circuits, etc.), the terms (including a reference to a “means”) used todescribe such components are intended to correspond, unless otherwiseindicated, to any component which performs the specified function of thedescribed component (i.e., that is functionally equivalent), even thoughnot structurally equivalent to the disclosed structure which performsthe function in the herein illustrated exemplary embodiments of theinvention. In addition, while a particular feature of the invention mayhave been disclosed with respect to only one of several embodiments,such feature may be combined with one or more other features of theother embodiments as may be desired and advantageous for any given orparticular application. Furthermore, to the extent that the term“includes” is used in either the detailed description and the claims,such term is intended to be inclusive in a manner similar to the term“comprising.”

1. An overvoltage protection circuit, comprising: one or more hard diskdrive integrated circuit chips residing on a board; a first voltagesupply potential for supplying power to at least one of the one or morehard disk drive integrated circuit chips; a second voltage supplypotential having an intended value which is less than the first voltagesupply potential, the second voltage supply potential for supplyingpower to at least one of the one or more hard disk drive integratedcircuit chips; a voltage detection circuit operable to detect a value ofthe second voltage supply potential; and a voltage reduction circuitoperably coupled to the voltage detection circuit, wherein the voltagedetection circuit is operable to activate the voltage reduction circuitwhen the second voltage supply potential exceeds a predeterminedthreshold, and wherein the voltage reduction circuit is operable toreduce the value of the second supply potential when activated by thevoltage detection circuit, further comprising a reset circuit coupled tothe voltage detection circuit, wherein the reset circuit is operable toactivate a reset signal to a controller circuit associated with theboard to reset the first and second voltage supply potentials when thevoltage detection circuit detects a first voltage supply potential whichexceeds an another predetermined threshold, and wherein the voltagedetection circuit further comprises a resistor coupled in series with azener diode, wherein when the zener diode has a reverse bias voltagethereacross which exceeds the predetermined threshold, the zener diodebreaks down and conducts current therethrough, thereby generating avoltage across the resistor, and wherein when the voltage across theresistor exceeds a predetermined level, the voltage activates thevoltage reduction circuit.
 2. The overvoltage protection circuit ofclaim 1, further comprising a first transistor coupled between thesecond voltage supply potential and a trace which transmits the secondvoltage supply potential to at least one of the one or more hard diskdrive integrated circuit chips, and wherein the first transistor has acontrol terminal coupled to the first voltage supply potential, andwherein the voltage reduction circuit comprises a second transistorcoupled to the control terminal of the first transistor and having acontrol terminal coupled to the resistor of the voltage detectioncircuit, wherein when the voltage across the resistor in the voltagedetection circuit exceeds the predetermined level, the second transistorturns on and lowers a voltage of the control terminal of the firsttransistor, thereby reducing a conduction of the first transistor andreducing a voltage value provided by the second voltage supply potentialto the trace.
 3. An overvoltage protection circuit, comprising: one ormore hard disk drive integrated circuit chips residing on a board; afirst voltage supply potential for supplying power to at least one ofthe one or more hard disk drive integrated circuit chips; a secondvoltage supply potential having an intended value which is less than thefirst voltage supply potential, the second voltage supply potential forsupplying power to at least one of the one or more hard disk driveintegrated circuit chips; a voltage detection circuit operable to detecta value of the first voltage supply potential; and a voltage reductioncircuit operably coupled to the voltage detection circuit, wherein thevoltage detection circuit is operable to activate the voltage reductioncircuit when the first voltage supply potential exceeds a predeterminedthreshold, and wherein the voltage reduction circuit is operable toreduce said value of the first supply potential when activated by thevoltage detection circuit, further comprising a reset circuit coupled tothe voltage detection circuit, wherein the reset circuit is operable toactivate a reset signal to a controller circuit associated with theboard to reset the first and second voltage supply potentials when thevoltage detection circuit detects a first voltage supply potential whichexceeds the predetermined threshold, wherein the voltage reductioncircuit comprises: a first transistor having a backgate diode associatedtherewith; and a second transistor having a backgate diode associatedtherewith, wherein the first and second transistor are coupled togetherin series in such a manner that the backgate diodes are oriented withrespect to one another in a back-to-back fashion, thereby preventingconduction therethrough under overvoltage conditions when the first andsecond transistors are biased in a substantially resistive conditionbased on an activation signal from the voltage detection circuit.
 4. Theovervoltage protection circuit of claim 3, wherein a back-to-backorientation of the backgate diodes comprises a configuration where acathode terminal of the backgate diodes are coupled together or aconfiguration where an anode terminal of the backgate diodes are coupledtogether.
 5. An overvoltage protection circuit for a hard disk drivecircuit board, comprising: one or more hard disk drive integratedcircuit chips residing on the board; a first voltage supply potentialfor supplying power to at least one of the hard disk drive integratedcircuit chips; a second voltage supply potential for supplying power toat least one of the hard disk drive integrated circuit chips, whereinthe second voltage supply potential has an intended value which is lessthan the first voltage supply potential; a first transistor coupledbetween the first voltage supply potential and a trace for transmittingthe first voltage supply potential to the at least one hard disk driveintegrated circuit chip, wherein when the first transistor issubstantially conducting, the first voltage supply potential istransmitted substantially to the trace, and wherein when the firsttransistor is not conducting substantially, a substantial voltage dropexists thereacross and a voltage potential transmitted to the trace isless than the first voltage supply potential; a zener diode coupled tothe first transistor and operable to be reverse biased and nonconductingwhen a value of the first voltage supply potential is less than apredetermined level, and wherein the zener diode is operable to breakdown and conduct current therethrough when the value of the firstvoltage supply potential is greater than or equal to the predeterminedlevel; a resistor coupled in series with the zener diode and operable toexhibit a voltage thereacross when the zener diode is conductingcurrent; and a second transistor coupled between the control terminal ofthe first transistor and one terminal of the resistor, and a controlterminal of the second transistor coupled to the other terminal of theresistor, wherein when the zener diode conducts current due to the firstvoltage supply potential exceeding the predetermined level, a voltagedevelops across the resistor and causes the second transistor toconduct, and wherein the conduction of the second transistor causes aconduction of the first transistor to be reduced, thereby reducing thevoltage at the trace, further comprising a reset circuit coupled to avoltage detection circuit, wherein the reset circuit is operable toactivate a reset signal to a controller circuit associated with theboard to reset the first and second voltage supply potentials when thevoltage detection circuit detects a first voltage supply potential whichexceeds the predetermined level.
 6. The overvoltage protection circuitof claim 5, further comprising a third transistor coupled in seriesbetween the first transistor and the zener diode, and wherein the firstand third transistors have backgate diodes associated therewith in whichthe backgate diodes are oriented in a back-to-back configuration,thereby preventing conduction therethrough when the first and thirdtransistors are biased in a substantially resistive condition based onan activation of the second transistor when an overvoltage condition isdetected.